For how long does the Apple Watch receive GPS position updates from my iPhone?

When you're using ForeFlight Mobile on the Apple Watch, ForeFlight Mobile on the iPhone keeps monitoring your GPS location in the background to speed up acquisition time for future openings of ForeFlight on the Apple Watch (ie: if used often, such as in-flight).

After about 20 minutes of not using ForeFlight on the Apple Watch, ForeFlight Mobile on your iPhone will stop monitoring your GPS position for the Apple Watch.